JPH06180102A - Controller for amount of boiler feedwater - Google Patents

Abstract

PURPOSE:To reduce the power loss of a feedwater pump and obtain an opening most suitable for a water-pouring valve, by a method wherein control signals for control means of the feedwater pump, a differential pressure-regulating valve for feedwater, and the water-pouring valve are separately compensated by a signal based on a multifuel firing ratio of a gaseous fuel for a boiler to an oil fuel therefor. CONSTITUTION:A differential pressure-regulating valve 3 for feedwater is controlled by an output signal obtained from the addition of following two signals through an adder 22. One is a detecting signal 25 for the rate of feedwater flow from a transmitter 15 for the rate of main steam flow and the other is an output signal from a proportional operation device 5, on the basis of both an output from a transmitter 4 for a differential pressure by the feedwater and an output from a differential pressure-presetting device 7. A water-pouring valve 23 for desuperheater 10 by poured water provided at the outlet of a primary superheater 9 is controlled by an output signal obtained from the addition of following signals through an adder 12. One is an output signal from a control operation device 13 for maintaining a main steam temperature constant and the other is a multifuel firing ratio-compensating signal 28 obtained from a max. objective valve 26 for the rate of poured water flow based on the detecting signal 25, multiplied by a multifuel firing ratio signal 27. The rotary speed of a feedwater pump 1 controlled by a presetting signal for the rate of the feedwater flow from a feedwater demand 19 and the opening of both the differential pressure valve 3 and the water-pouring valve 23 are compensated by this compensating signal 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler water supply amount control device, and more particularly to a water supply amount control device for a boiler, which is suitable for securing a necessary water supply amount for a water injection desuperheater and reducing operating power. Regarding the control device.

[0002]

2. Description of the Related Art A conventional boiler water supply amount control device is shown in FIG.
As shown in, the rotation speed of the boiler feed water pump 1 is controlled by the deviation between the feed water flow rate setting signal from the water feed demand 19 and the feed water flow rate detection signal based on the signal from the main steam flow rate transmitter 15, and the feed water differential pressure valve 3 Is controlled to a constant differential pressure by the feed water differential pressure transmitter 4 and the differential pressure setting device 7, and the desuperheater water injection valve 2
3 was controlled by the main steam thermometer 24 so as to keep the main steam temperature constant, and each was controlled independently. FIG. 6 shows the relationship between the required water injection flow rate (during gas-only firing and oil-only firing) and the required water injection pressure for the water injection desuperheater 10. Generally, when gas fuel is exclusively burned, the volume of combustion products is larger than when oil is exclusively burned, the gas velocity in the superheater and reheater provided in the rear area of the boiler furnace is large, and the amount of heat absorbed by convective heat transfer is large. Therefore, since the steam temperature of the superheater becomes too high, the amount of water injected into the water injection desuperheater is increased to control the boiler outlet steam temperature to a predetermined value.

In each of the conventional independent control methods described above, the rotation speed of the boiler feed water pump 1 and the opening degree of the feed water differential pressure valve 3 are always controlled on the assumption of the maximum water injection amount (when gas fuel is exclusively burned). . In other words, a control circuit that minimizes the power consumption of the water supply pump by coordinating the boiler water supply pump rotation speed and the water supply differential pressure valve opening degree in response to the required water injection pressure that changes depending on the type of fuel used and the mixed combustion ratio was not considered. .

[0004]

SUMMARY OF THE INVENTION In the above-mentioned prior art, the power consumption of the water supply pump is minimized by performing the water supply pump speed control and the water supply differential pressure valve opening control according to the change of the desuperheater water injection flow rate required value. Is not taken into consideration, and assuming the condition that the desuperheater water injection amount is maximum (maximum water injection flow rate during gas combustion), determine the differential pressure setting value of the feed water differential pressure valve and the boiler feed water pump speed, The same settings were used even when the gas was not exclusively burned. Water will be supplied at a pressure that is higher than the required water injection pressure in any state other than during gas combustion.
Since this extra water injection pressure is absorbed by squeezing the water injection valve, there was a problem that the power consumption of the boiler supply pump was lost and the water injection valve had to be operated at a low opening.

It is an object of the present invention to provide a boiler water supply amount control device which can reduce the loss of power consumption of a boiler water supply pump and can always obtain an optimum water injection valve opening.

[0006]

In order to achieve the above object, the first invention of the present application is to control the rotation speed of a boiler feed water pump so as to discharge the feed water corresponding to the evaporation amount of the boiler on the basis of a signal from the feed water demand. Water supply pump control means and a water supply differential pressure valve control means for controlling the amount of water supply discharged from the water supply pump based on the differential pressure detection value before and after that so as to secure the required water supply amount for the boiler and the water injection pressure for the water injection desuperheater. In the boiler water supply amount control device including a water injection valve control means for controlling the water injection amount to the water injection desuperheater based on the detected value of the main steam temperature, the water supply pump control means, the water supply differential pressure valve control means, and water injection The present invention relates to a boiler water supply amount control device, which is provided with means for correcting each control signal of the valve control means by a signal based on a mixed combustion ratio of gas fuel and oil fuel of the boiler.

A second aspect of the present invention provides a means for controlling the boiler feed water pump based on a signal from the water supply demand, a means for controlling the feed water differential pressure valve based on the differential pressure detection value before and after it, and a main steam temperature detection value. In a boiler water supply amount control device including a water injection valve control means that operates based on the above, a means for generating a water supply flow rate detection signal, a means for calculating a water injection amount maximum target value based on the water supply flow rate detection signal, and this water injection amount Means for generating a mixed combustion ratio correction signal by multiplying the maximum target value by the mixed combustion ratio of gas fuel and oil in the boiler, means for controlling the boiler feed water pump by the mixed combustion ratio correction signal and the signal from the water supply demand, Means for controlling the feed water differential pressure valve by the signal from the differential pressure setting device based on the mixed combustion ratio correction signal, the differential pressure signal across the feed water differential pressure valve, and the feed water flow rate detection signal; and the main steam temperature detection About feedwater flow control system of the boiler, characterized in that a means for controlling the water injection control valve based on the No. and mixed combustion ratio correction signal.

[0008]

The calculated or manually set oil-gas mixed combustion ratio signal operates so as to give the boiler feed water pump rotation speed and the water injection valve opening corresponding to the required water injection amount and water injection pressure during the mixed combustion. As a result, the water supply pump operates at the required minimum speed, and the water injection valve is controlled at an appropriate opening, so that the loss of operating power is minimized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the entire system of a boiler water supply amount control apparatus showing an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the required flow rate of water supplied to the desuperheater and the fluid pressure of each part in the boiler. FIG. 3 is a diagram showing the characteristics of the calculator and the feed water differential pressure valve shown in FIG. In FIG. 1, the water supply pump 1 discharges the water supply corresponding to the boiler evaporation amount by varying the speed in accordance with the water supply flow rate setting signal from the water supply demand 19 that outputs a signal according to the boiler load, and It is controlled to keep the water level constant. The water supply differential pressure valve 3 is for the purpose of ensuring the required water supply amount to the boiler and the water injection pressure to the desuperheater, the water supply flow rate detection signal 25 based on the main steam flow transmitter 15, the water supply differential pressure transmitter 4 and the differential pressure setting device 7. It is controlled by the output of the adder 22 that adds the output signal from the comparison calculator 5 based on. The water injection valve 23 for the water injection desuperheater 10 provided at the outlet of the primary superheater 9 supplies the water supplied by the signal from the main steam flow rate transmitter 15 to the output of the control calculator 13 for controlling the main steam temperature at a constant level. Flow rate detection signal 25
It is controlled by the output of the adder 12 which adds the mixed combustion ratio correction signal 28 obtained by multiplying the maximum water injection target value 26 based on the above by the signal from the mixed combustion ratio setter 18. The output of the main steam flow rate transmitter 15 provided at the boiler outlet is converted by the switch 16 into the feed water flow rate detection signal 25, and the function generator 14 forms the maximum target value 26 (when gas is exclusively burned) of the water injection amount. The maximum target value 26 of the water amount and the mixed combustion ratio signal 27 from the mixed combustion ratio setting device 18 are used as the mixed combustion ratio correction signal 28 in the multiplier 17 to change the rotation speed of the boiler feed water pump 1, the feed water differential pressure valve 3 and the opening degree of the water injection valve 23. Let Output signal 2 of the function generator 14 which transmits the maximum water injection demand setting signal of the gas-only firing base
By multiplying 6 by the mixed burning ratio signal 27,
Compared to the maximum control value, the boiler feed water pump speed decreases, power loss decreases, the opening degree of the feed water differential pressure valve 3 increases, pressure loss decreases, the opening degree of the water injection valve 23 increases, and control characteristics are good. The amount of water supply and the amount of water injection are controlled with various valve openings.

FIG. 4 shows the boiler load vs. boiler feed water pump rotation speed and feed water differential pressure valve opening characteristics when the present invention is implemented. The hatched portion shows an improvement as compared with the prior art. In other words, the boiler feed water pump rotation speed is always equal to or less than that of the conventional technique, and the feed water differential pressure valve opening is large. The inlet pressure required value of the feed water differential pressure valve 3 in accordance with the change of the mixed combustion ratio exists between the gas exclusive combustion and the oil exclusive combustion of the characteristic curve of FIG. The desuperheater water injection flow rate also exists between the maximum time (when gas is exclusively burned) and the minimum time (when oil is exclusively burned). In the present embodiment, the function generator 14 first creates a maximum water injection amount target signal 26 (when gas is exclusively burned) based on the signal from the main steam flow transmitter 15. This maximum target signal is multiplied by the gas mixed combustion ratio signal 27 by the multiplier 17, and the multiplier 1
The output of 7 is added to the water supply demand 19 which is the rotation speed control signal of the boiler water supply pump by the adder 20 to control the water supply pump rotation speed drive 2. Similarly, by giving it to the adder 12 as the target preceding value of the water injection valve 23, it is possible to obtain an operating state according to the mixed combustion ratio at that time.

The water supply differential pressure valve 3 inputs the output of the multiplier 17 to the differential pressure setting device 7 to cause the differential pressure valve opening to operate in the opposite direction to the required water injection amount. That is, when the water injection amount required value (26) increases, the response is increased, so that the feed water differential pressure set value is increased and the feed water differential pressure valve opening is decreased. In the above embodiment, the feed water flow rate detection signal 25 is obtained based on the signal from the main steam flow rate transmitter 15, but it may be obtained from the feed water flow rate detector 29 provided downstream of the feed water differential pressure valve 3.

[0012]

According to the present invention, the conventional water supply pump, the water supply differential pressure valve, and the water injection valve are used for the one having a characteristic that the desuperheater water injection flow rate required value in the mixed-fired boiler greatly changes, It is possible to obtain an operating state in which the power loss of the boiler feed water pump is minimized and the water injection valve opening is in a position with good controllability without making a particularly large change.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a desuperheater water injection flow rate and a feed water differential pressure valve inlet pressure with respect to a boiler load in the present invention.

FIG. 3 is a diagram showing control signals for a water supply pump and a water supply differential pressure valve in the embodiment of the present invention.

FIG. 4 is a diagram showing an effect of the present invention.

[Fig. 5]

FIG. 6 is a diagram showing a conventional technique.

[Explanation of symbols]

1 ... Water supply pump, 2 ... Water supply pump drive, 3 ... Water supply differential pressure valve, 4 ... Water supply differential pressure transmitter, 5 ... Comparison calculator, 7 ... Differential pressure setting device, 8 ... Drum, 9 ... Primary superheater, 10 ... Water injection desuperheater, 11 ... Secondary superheater, 12 ... Adder, 13 ... Control calculator, 14 ... Function generator, 15 ... Main steam flow transmitter, 16
... Switch, 17 ... Multiplier, 18 ... Mixture ratio setting device, 19
... Water supply demand, 20 ... Adder, 22 ... Adder, 23 ...
Water injection valve, 24 ... Main steam thermometer, 25 ... Water supply flow rate detection signal, 26 ... Water injection amount maximum target value, 27 ... Mixed combustion ratio signal, 2
8 ... Mixed burning ratio correction signal.

Claims (2)

[Claims] 1. A water supply pump control means for controlling the number of revolutions of a boiler water supply pump so as to discharge water supply corresponding to a boiler evaporation amount based on a signal from a water supply demand, and a necessary water supply amount for a boiler and a water injection desuperheater. Water supply differential pressure valve control means for controlling the amount of water supply discharged from the water supply pump based on the differential pressure detection value before and after that so as to ensure the water injection pressure,
In a boiler water supply amount control device equipped with a water injection valve control means for controlling an amount of water injection to a water injection desuperheater based on a detected value of a main steam temperature, said water supply pump control means, water supply differential pressure valve control means, and water injection valve control A boiler water supply amount control device comprising means for correcting each control signal of the means by a signal based on a mixed combustion ratio of gas fuel and oil fuel of the boiler. 2. A means for controlling a boiler feed pump based on a signal from a water supply demand, a means for controlling a feed water differential pressure valve based on a differential pressure detection value before and after it, and a water injection which operates based on a detected value of a main steam temperature. In a boiler water supply amount control device having a valve control means, a means for generating a water supply flow rate detection signal, a means for calculating a water injection amount maximum target value based on the water supply flow rate detection signal, and the water injection amount maximum target value Means for generating a mixed combustion ratio correction signal by multiplying the mixed combustion ratio of gas fuel and oil in the boiler, means for controlling the boiler feed water pump by the mixed combustion ratio correction signal and the signal from the water supply demand, and a mixed combustion ratio correction signal Means for controlling the feed water differential pressure valve by the signal from the differential pressure setting device based on the above, the differential pressure signal across the feed water differential pressure valve, and the feed water flow rate detection signal, and the main steam temperature detection signal and the mixed combustion ratio And a means for controlling a water injection control valve on the basis of a correction signal.